Method for calculating height of air inlet channel separation channel of wind tunnel model

Abstract

The invention discloses a wind tunnel model air inlet channel separation channel height calculation method, and belongs to the technical field of wind tunnel tests. In order to improve the accuracy of a wind tunnel test result, a Reynolds number calculation formula suitable for engineering is constructed; calculating the Reynolds number at the inlet of the air inlet of the aircraft; calculating the Reynolds number at the inlet of the air inlet of the wind tunnel model; constructing a boundary layer thickness calculation formula; calculating the thickness of a boundary layer at the inlet of the air inlet of the aircraft; calculating the thickness of a boundary layer at the inlet of the wind tunnel model air inlet; calculating the ratio of the aircraft to the thickness of the boundary layer at the inlet of the wind tunnel model; and based on the obtained ratio of the aircraft to the thickness of the boundary layer at the inlet of the air inlet of the wind tunnel model, calculating the air inlet separation height of the wind tunnel model. According to the method, the air inlet channel separation channel height scaling ratio is determined according to the boundary layer thickness similarity principle, the problem that the air inlet channel performance is low due to the fact that part of low-energy boundary layers are sucked into the air inlet channel when the air inlet channel separation channel height scaling ratio is small according to the geometric similarity principle is solved, and the accuracy of test data is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tunnel tests, and in particular relates to a method for calculating the height of an air inlet partition of a wind tunnel model. Background Art

[0002] The low-energy boundary layer generated by the front fuselage of the aircraft entering the air inlet will cause the performance of the aircraft to decrease. The function of the air inlet partition of the aircraft is to discharge the low-energy boundary layer and prevent it from entering the air inlet. Usually, the height of the air inlet partition of the wind tunnel model is scaled according to the principle of geometric similarity. If the ratio of the geometric dimensions of the real aircraft to the geometric dimensions of the wind tunnel model is 10:1, the height of the air inlet partition of the wind tunnel model is also reduced to 1 / 10 of the original. However, since the Reynolds number cannot be kept constant in the flow field around the wind tunnel model and the real aircraft, and the Reynolds number in the wind tunnel is low, the thickness of the boundary layer on the fuselage near the air inlet of the wind tunnel model is not reduced by 10 times, and the reduction ratio is usually less than 10 times, which does not follow the principle of geometric similarity and is different from the actual boundary layer thickness on the aircraft. The height of the air inlet partition of the real aircraft can effectively discharge the low-energy boundary layer, while the height of the air inlet partition of the wind tunnel model according to the geometric scale cannot completely discharge the low-energy boundary layer, which may lead to the low air inlet performance obtained by the wind tunnel test and the conservative test results. Summary of the invention

[0003] The problem to be solved by the present invention is to improve the accuracy of wind tunnel test results and to propose a method for calculating the height of an air inlet partition of a wind tunnel model.

[0004] To achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A method for calculating the height of an air inlet partition of a wind tunnel model comprises the following steps:

[0006] S1. Construct a Reynolds number calculation formula suitable for engineering;

[0007] S2. Calculate the Reynolds number at the entrance of the aircraft air inlet based on the Reynolds number calculation formula applicable to the project obtained in step S1;

[0008] S3. Calculate the Reynolds number at the inlet entrance of the wind tunnel model based on the Reynolds number calculation formula applicable to the project obtained in step S1;

[0009] S4. Based on the Reynolds number calculation formula applicable to engineering obtained in step S1, a boundary layer thickness calculation formula is constructed;

[0010] S5. Calculate the boundary layer thickness at the inlet of the aircraft based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the aircraft obtained in step S2;

[0011] S6. Calculate the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the wind tunnel model obtained in step S3;

[0012] S7. Calculate the ratio of the boundary layer thickness at the inlet of the aircraft to the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness at the inlet of the aircraft obtained in step S5 and the boundary layer thickness at the inlet of the wind tunnel model obtained in step S6;

[0013] S8. Calculate the air inlet separation height of the wind tunnel model based on the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model obtained in step S7.

[0014] Furthermore, the specific implementation method of step S1 to construct a Reynolds number calculation formula suitable for engineering includes the following steps:

[0015] S1.1. Under normal conditions, the calculation formula for setting the Reynolds number is:

[0016]

[0017] Among them, Re L is the Reynolds number with L as the characteristic length, U is the incoming flow velocity, ρ is the local air density, μ is the dynamic viscosity coefficient of the local air, and L is the characteristic length;

[0018] S1.2. Solve for various parameters in the conventional Reynolds number calculation formula;

[0019] The relationship between total temperature and static temperature is set as follows:

[0020] T0=T·(1+0.2M 2 )

[0021] Where T0 is the local total air temperature, T is the local static air temperature, and M is the local Mach number;

[0022] The calculation formula for the incoming flow velocity U is set as:

[0023] U=M·a

[0024] Where a is the local speed of sound;

[0025] The calculation formula for setting the local sound speed a is:

[0026]

[0027] Where r is the adiabatic index; R is the gas constant, and T is the local static temperature;

[0028] The relationship between total pressure and static pressure is set as:

[0029] P0=P·(1+0.2M2 ) 3.5

[0030] Among them, P0 is the local total air pressure, and P is the local static air pressure;

[0031] Set the local air density calculation formula to:

[0032]

[0033] The calculation formula of kinematic viscosity coefficient is set as:

[0034]

[0035] S1.3. Based on the formula in step S1.2, derive the formula for calculating the Reynolds number:

[0036]

[0037] Furthermore, step S2 calculates the Reynolds number Re at the entrance of the aircraft inlet duct L飞行器 The formula is:

[0038]

[0039] Among them, M 飞行器 is the Mach number of the aircraft, P 0飞行器 is the total pressure of the aircraft at a specified flight altitude, L 飞行器 is the characteristic length of the aircraft, T 0飞行器 is the total temperature of the aircraft at a specified flight altitude.

[0040] Further, step S3 calculates the Reynolds number Re at the inlet of the wind tunnel model L风洞模型 The formula is:

[0041]

[0042] Among them, T 0风洞模型 is the total temperature of the wind tunnel test section, obtained by actual measurement; P 0风洞模型 is the total pressure of the wind tunnel test section, obtained by actual measurement; L 风洞模型 is the characteristic length of the wind tunnel model, M 风洞模型 is the Mach number of the wind tunnel test;

[0043] M 风洞模型 =M 飞行器 .

[0044] Furthermore, the boundary layer thickness calculation formula constructed in step S4 is:

[0045]

[0046] Here, δ is the boundary layer thickness.

[0047] Furthermore, the formula for calculating the boundary layer thickness at the entrance of the aircraft air inlet in step S5 is:

[0048]

[0049] Among them, δ 飞行器 is the boundary layer thickness at the inlet entrance of a real aircraft.

[0050] Furthermore, the formula for calculating the boundary layer thickness at the inlet of the wind tunnel model in step S6 is:

[0051]

[0052] Among them, δ 风洞模型 is the boundary layer thickness at the inlet entrance of the wind tunnel model.

[0053] Furthermore, the formula for calculating the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model in step S7 is:

[0054]

[0055] Among them, λ 边界层 is the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model.

[0056] Furthermore, the formula for calculating the height of the air inlet partition of the wind tunnel model in step S8 is:

[0057]

[0058] Among them, H 风洞模型 is the height of the wind tunnel model inlet duct separation, H 飞行器 It is the separation height of the aircraft air inlet.

[0059] Beneficial effects of the present invention:

[0060] The method for calculating the height of the air intake partition of a wind tunnel model described in the present invention determines the scaling ratio of the air intake partition height according to the principle of similarity of the boundary layer thickness, thereby solving the problem that the air intake partition height is scaled too small according to the principle of geometric similarity, causing part of the low-energy boundary layer to be sucked into the air intake, thereby resulting in low air intake performance, and improving the accuracy of the air intake test data.

[0061] The method for calculating the height of the air inlet partition of a wind tunnel model described in the present invention is suitable for engineering calculations, can quickly estimate the height of the air inlet partition of the wind tunnel model and the scaling ratio, and provide technical guidance for the design of the wind tunnel model. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1The present invention provides a flow chart of a method for calculating the height of an air inlet partition of a wind tunnel model. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0064] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0065] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 The detailed instructions are as follows:

[0066] Example:

[0067] A method for calculating the height of an air inlet partition of a wind tunnel model comprises the following steps:

[0068] S1. Construct a Reynolds number calculation formula suitable for engineering;

[0069] Furthermore, the specific implementation method of step S1 to construct a Reynolds number calculation formula suitable for engineering includes the following steps:

[0070] S1.1. Under normal conditions, the calculation formula for setting the Reynolds number is:

[0071]

[0072] Among them, Re L is the Reynolds number with L as the characteristic length, U is the incoming flow velocity, ρ is the local air density, μ is the dynamic viscosity coefficient of the local air, and L is the characteristic length;

[0073] S1.2. Solve for various parameters in the conventional Reynolds number calculation formula;

[0074] The relationship between total temperature and static temperature is set as follows:

[0075] T0=T·(1+0.2M2 )

[0076] Where T0 is the local total air temperature, T is the local static air temperature, and M is the local Mach number;

[0077] The calculation formula for the incoming flow velocity U is set as:

[0078] U=M·a

[0079] Where a is the local speed of sound;

[0080] The calculation formula for setting the local sound speed a is:

[0081]

[0082] Wherein, r is the adiabatic index, which is 1.4 for air; R is the gas constant, which is 287.053 N·m / (Kg·K) for air;

[0083] The relationship between total pressure and static pressure is set as:

[0084] P0=P·(1+0.2M 2 ) 3.5

[0085] Among them, P0 is the local total air pressure, and P is the local static air pressure;

[0086] Set the local air density calculation formula to:

[0087]

[0088] The calculation formula of kinematic viscosity coefficient is set as:

[0089]

[0090] S1.3. Based on the formula in step S1.2, derive the formula for calculating the Reynolds number:

[0091]

[0092] Furthermore, the geometric similarity scaling ratio λ between the aircraft and the wind tunnel model is calculated 几何 , the calculation formula is:

[0093]

[0094] Among them, L 飞行器 is the characteristic length of the aircraft, L 风洞模型 is the characteristic length of the wind tunnel model, L 飞行器 With L 风洞模型 The characteristic length corresponds to the characteristic length from the nose to the inlet of the air inlet or the diameter length of the outlet of the air inlet;

[0095] λ 几何 It is usually obtained by weighing and limiting multiple factors such as the test purpose, wind tunnel test section size, wind tunnel blockage, and the simulation capability of the internal flow test equipment. 几何 Usually 5 to 20 are selected, 几何 The larger the value, the smaller the wind tunnel model size.

[0096] S2. Calculate the Reynolds number at the entrance of the aircraft air inlet based on the Reynolds number calculation formula applicable to the project obtained in step S1;

[0097] Furthermore, step S2 calculates the Reynolds number Re at the entrance of the aircraft inlet duct L飞行器 The formula is:

[0098]

[0099] Among them, M 飞行器 is the Mach number of the aircraft, P 0飞行器 is the total pressure of the aircraft at a specified flight altitude, L 飞行器 is the characteristic length of the aircraft, T 0飞行器 is the total temperature of the aircraft at a specified flight altitude.

[0100] S3. Calculate the Reynolds number at the inlet entrance of the wind tunnel model based on the Reynolds number calculation formula applicable to the project obtained in step S1;

[0101] Further, step S3 calculates the Reynolds number Re at the inlet of the wind tunnel model L风洞模型 The formula is:

[0102]

[0103] Among them, T 0风洞模型 is the total temperature of the wind tunnel test section, obtained by actual measurement; P 0风洞模型 is the total pressure of the wind tunnel test section, obtained by actual measurement; L 风洞模型 is the characteristic length of the wind tunnel model, M 风洞模型 is the Mach number of the wind tunnel test;

[0104] M 风洞模型 =M 飞行器 .

[0105] S4. Based on the Reynolds number calculation formula applicable to engineering obtained in step S1, a boundary layer thickness calculation formula is constructed; further, the boundary layer thickness calculation formula constructed in step S4 is:

[0106]

[0107] Here, δ is the boundary layer thickness.

[0108] S5. Calculate the boundary layer thickness at the inlet of the aircraft based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the aircraft obtained in step S2;

[0109] Furthermore, the formula for calculating the boundary layer thickness at the entrance of the aircraft air inlet in step S5 is:

[0110]

[0111] Among them, δ 飞行器 is the boundary layer thickness at the inlet entrance of a real aircraft.

[0112] S6. Calculate the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the wind tunnel model obtained in step S3;

[0113] Furthermore, the formula for calculating the boundary layer thickness at the inlet of the wind tunnel model in step S6 is:

[0114]

[0115] Among them, δ 风洞模型 is the boundary layer thickness at the inlet entrance of the wind tunnel model.

[0116] S7. Calculate the ratio of the boundary layer thickness at the inlet of the aircraft to the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness at the inlet of the aircraft obtained in step S5 and the boundary layer thickness at the inlet of the wind tunnel model obtained in step S6;

[0117] Furthermore, the formula for calculating the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model in step S7 is:

[0118]

[0119] Among them, λ 边界层 is the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model.

[0120] S8. Calculate the height of the wind tunnel model inlet duct partition based on the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model obtained in step S7;

[0121] Furthermore, the formula for calculating the height of the air inlet partition of the wind tunnel model in step S8 is:

[0122]

[0123] Among them, H 风洞模型 is the height of the wind tunnel model inlet duct separation, H 飞行器 It is the separation height of the aircraft air inlet.

[0124] The practical application cases using the method of Example 1 are as follows:

[0125] A method for scaling the height of the air intake partition of a wind tunnel model. The steps of this method are shown in Figure 1 , the specific steps are as follows:

[0126] Determine the geometric similarity scale between the aircraft and the wind tunnel model:

[0127] Assume that the geometric similarity scaling ratio between the aircraft and the wind tunnel model is determined according to the test requirements.

[0128] Derive the Reynolds number formula suitable for engineering calculations:

[0129]

[0130] Furthermore, the Reynolds number at the entrance of the aircraft air inlet is calculated;

[0131] Assume the aircraft is flying at an altitude of 11 km and the flight M 飞行器 =0.8, length from fuselage to air inlet entrance L 飞行器 = 10m, check the standard atmospheric property table, and get the atmospheric static temperature T = -56.5℃ = 216.65K and atmospheric static pressure P = 22610Pa at this height. The atmospheric total temperature T is calculated by the relationship formula between total temperature and static temperature. 0飞行器 =244.38K, the total atmospheric pressure P is calculated from the relationship between total pressure and static pressure 0飞行器 =34465Pa.

[0132] According to the formula Calculate Re L飞行器 =6.0374×10 7 .

[0133] Furthermore, the Reynolds number at the inlet entrance of the wind tunnel model is calculated:

[0134] In wind tunnel tests, the total pressure and total temperature are usually controllable and measurable, and are provided by actual measured values. Here, we assume that T 0风洞模型 =15℃=288.15K, total pressure It can be seen that L 风洞模型 =1m;M 风洞模型 =M 飞行器 =0.8.

[0135] thus Calculate Re L风洞模型 =1.5504×10 7 .

[0136] Furthermore, the boundary layer thickness calculation formula is derived based on the Reynolds number:

[0137] Turbulent boundary layer thickness calculation formula

[0138] Furthermore, the boundary layer thickness at the aircraft inlet entrance is estimated:

[0139]

[0140] Furthermore, the boundary layer thickness at the inlet entrance of the wind tunnel model is estimated:

[0141]

[0142] Furthermore, the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model is calculated:

[0143]

[0144] Furthermore, the height of the air inlet partition of the wind tunnel model is determined:

[0145] Assuming the height of the aircraft air inlet partition is 150mm,

[0146]

[0147] If scaling is performed based on geometric similarity, The height of the inlet duct partition is relatively low, and a low-energy boundary layer will be sucked into the inlet duct.

[0148] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0149] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for calculating the height of the air intake partition of a wind tunnel model, characterized in that: The steps include: S1. Construct a Reynolds number calculation formula suitable for engineering; S2. Calculate the Reynolds number at the entrance of the aircraft air inlet based on the Reynolds number calculation formula applicable to the project obtained in step S1; S3. Calculate the Reynolds number at the inlet entrance of the wind tunnel model based on the Reynolds number calculation formula applicable to the project obtained in step S1; S4. Based on the Reynolds number calculation formula applicable to engineering obtained in step S1, a boundary layer thickness calculation formula is constructed; S5. Calculate the boundary layer thickness at the inlet of the aircraft based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the aircraft obtained in step S2; S6. Calculate the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness calculation formula obtained in step S4 and the Reynolds number at the inlet of the wind tunnel model obtained in step S3; S7. Calculate the ratio of the boundary layer thickness at the inlet of the aircraft to the boundary layer thickness at the inlet of the wind tunnel model based on the boundary layer thickness at the inlet of the aircraft obtained in step S5 and the boundary layer thickness at the inlet of the wind tunnel model obtained in step S6; S8. Calculate the air inlet separation height of the wind tunnel model based on the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model obtained in step S7.

2. A method for calculating the height of the air intake duct of a wind tunnel model according to claim 1, characterized in that: Step S1: The specific implementation method of constructing a Reynolds number calculation formula suitable for engineering includes the following steps: S1.

1. Under normal conditions, the calculation formula for setting the Reynolds number is: Among them, Re L is the Reynolds number with L as the characteristic length, U is the incoming flow velocity, ρ is the local air density, μ is the dynamic viscosity coefficient of the local air, and L is the characteristic length; S1.

2. Solve for various parameters in the conventional Reynolds number calculation formula; The relationship between total temperature and static temperature is set as follows: T0=T·(1+0.2M 2 ) Where T0 is the local total air temperature, T is the local static air temperature, and M is the local Mach number; The calculation formula for the incoming flow velocity U is set as: U=M·a Where a is the local speed of sound; The calculation formula for setting the local sound speed a is: Where r is the adiabatic index; R is the gas constant; The relationship between total pressure and static pressure is set as: P0=P·(1+0.2M 2 ) 3.5 Among them, P0 is the local total air pressure, and P is the local static air pressure; Set the local air density calculation formula to: The calculation formula of kinematic viscosity coefficient is set as: S1.

3. Based on the formula in step S1.2, derive the formula for calculating the Reynolds number:

3. The method for calculating the height of the air intake partition of a wind tunnel model according to claim 2, characterized in that: Step S2 calculates the Reynolds number Re at the entrance of the aircraft inlet L飞行器 The formula is: Among them, M 飞行器 is the Mach number of the aircraft, P 0飞行器 is the total pressure of the aircraft at a specified flight altitude, L 飞行器 is the characteristic length of the aircraft, T 0飞行器 is the total temperature of the aircraft at a specified flight altitude.

4. The method for calculating the height of the air intake partition of a wind tunnel model according to claim 3 is characterized in that: Step S3 calculates the Reynolds number Re at the inlet of the wind tunnel model L风洞模型 The formula is: Among them, T 0风洞模型 is the total temperature of the wind tunnel test section, obtained by actual measurement; P 0风洞模型 is the total pressure of the wind tunnel test section, obtained by actual measurement; L 风洞模型 is the characteristic length of the wind tunnel model, M 风洞模型 is the Mach number of the wind tunnel test; M 风洞模型 =M 飞行器 。 5. A method for calculating the height of the air intake partition of a wind tunnel model according to claim 4, characterized in that: The boundary layer thickness calculation formula constructed in step S4 is: Here, δ is the boundary layer thickness.

6. A method for calculating the height of the air intake partition of a wind tunnel model according to claim 5, characterized in that: Step S5 calculates the boundary layer thickness at the entrance of the aircraft air inlet as follows: Among them, δ 飞行器 is the boundary layer thickness at the inlet entrance of a real aircraft.

7. A method for calculating the height of the air intake partition of a wind tunnel model according to claim 6, characterized in that: Step S6: The formula for calculating the boundary layer thickness at the inlet entrance of the wind tunnel model is: Among them, δ 风洞模型 is the boundary layer thickness at the inlet entrance of the wind tunnel model.

8. A method for calculating the height of the air intake partition of a wind tunnel model according to claim 7, characterized in that: Step S7 calculates the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model as follows: Among them, λ 边界层 is the ratio of the boundary layer thickness at the inlet entrance of the aircraft and the wind tunnel model.

9. A method for calculating the height of the air intake partition of a wind tunnel model according to claim 8, characterized in that: Step S8: The formula for calculating the height of the air inlet partition of the wind tunnel model is: Among them, H 风洞模型 is the height of the wind tunnel model inlet duct separation, H 飞行器 It is the separation height of the aircraft air inlet.

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